Solvents in coatings will only be environmentally friendly in the future

The solvent is an important component of solvent-based coatings. It is not only used to dissolve resins and reduce viscosity to improve manufacturing performance, but also affects the anticipated construction and performance of coatings. Solvent-based coatings are engineering coatings prepared with organic solvents as dispersing media. Although solvent-based coatings have some problems such as environmental pollution, energy waste and high cost, solvent-based coatings still have a certain range of applications, and have its own obvious advantages of coatingol.com online. First of all, from the performance comparison, solvent-based coatings still have a great advantage. Solvents are widely used in paint industry as important diluents. However, with the acceleration of environmental protection process, traditional organic solvents have become an important problem hindering the development of the industry because they contain toxic and harmful substances such as benzene, Toluene and xylene. During the 13th Five-Year Plan period, China will gradually impose strict restrictions on VOC emissions. Reducing the consumption of solvents or replacing toxic and harmful solvents with low toxic solvents has attracted wide attention in the coating industry. Solvents used to dissolve binders are beneficial to production and construction. They are volatile components of coatings and volatilize during the drying process of coatings. In order to obtain satisfactory results, mixed solvents are often used in practical production. The role of solvent in paint is often neglected. It is believed that solvent is volatile and will not remain in the film, so it has little effect on the quality of the film. In fact, the solubility and volatilization rate of various solvents will greatly affect the performance of paint production, storage, construction, film gloss, adhesion and surface state.

In the manufacture of coatings, two basic properties should be considered when selecting suitable solvents, i.e. solubility and volatilization rate. Solubility refers to the ability to dissolve coatings with solvents and reduce their viscosities to achieve application purposes. The solubility of solvents to binders can be based on empirical law: macromolecule compounds can be dissolved in low molecular solvents with similar structure; liquids with equal or similar cohesive energy density can be well soluble with each other. Solvents can be divided into main solvents (active solvents), cosolvents and diluents according to their roles in coatings. The main (active) solvent dissolves the resin, makes the resin solution and uses it as the paint of the paint. Many synthetic resins are solid, including most alkyd resins, some epoxy resins, chlorinated rubber resins and vinyl resins. The cosolvent is usually used with the main solvent to make the coating easy to construct, control the volatilization rate and improve the quality of the final film. There are many solvents that can not dissolve the resins used in coatings independently, but by mixing them with some good solvents, they can obtain the same or greater solubility as the good solvents. These solvents become cosolvents, also known as latent solvents. For example, alcohols alone can not dissolve nitrocellulose, but they can be mixed with ketones and esters in a certain proportion to obtain greater solubility, so alcohols are co-solvents of nitrocellulose. The diluent is mainly used to dilute the ready-made coatings and reduce the viscosity of the coatings to facilitate construction. It is a mixed solvent composed of a variety of solvents. The selection principle of diluent is that it has good solubility, can volatilize from the coating film with the drying of the coating film, no non-volatile residues, and is easy to mix with the solvent. At the same time, the toxicity and flammability of the diluent should be considered. Solvents account for 30%-50% of the total volume of conventional liquid coatings. The main roles of solvents in coatings are as follows: dissolving and dispersing the resin in coatings, adjusting its viscosity and rheological properties, making it easy to paint; increasing the storage stability of coatings; improving the appearance of coatings, such as gloss and fullness; increasing the wettability of coatings on the coated substrates and increasing their adhesion; and composing a reasonable volatilization rate. Give the paint the best fluidity and leveling. Different resin series can only dissolve in different active solvents. In the same paint formulation, a variety of resins are often used, so the combination of various active solvents can achieve better results.

Principles for formulation of paint solvents:

Achieve the most stable and optimum balance among the active solvents, and add as many filling solvents as possible to optimize the cost and adjust the construction viscosity. In order to meet the increasingly stringent environmental requirements, low VOC latex paint, Water-borne paint, UV-curable paint and powder coatings have developed rapidly, but solvent-based coatings still occupy a very important position in the field of coatings because of their performance and construction advantages. Paint solvent is one of the most important components in the formulation system of coatings, accounting for about 30%-50% of the proportion of the coating system. In the golden age of solvent-based coatings, the effect of solvents on paint formulations is more important than the solubility of paint resins in solvents. However, with the advent of the era of low VOC, the traditional organic solvents began to appear a new round of crisis. Due to legal and economic reasons, solvents have been limited to adverse conditions because of their defects as physical substances. They are expensive, easy to run around and inconvenient to clean, most of them are flammable to some extent and may cause explosion danger, many of them are harmful... The use of solvents in the world has resulted in the loss of precious petroleum resources, and when used improperly, it will do more harm than good. Whether in terms of economic cost or environmental responsibility, the paint industry needs to re-examine the current paint solvent market